Biological samples may be preserved by cryogenic freezing. The biological samples are usually stored in disposable containers (disposables). The shape of the disposable container used depends on the type of sample. Examples of commonly used disposable containers include vials, straws and bags. The disposable container is stored at low temperatures in a Dewar flask, usually filled with liquid nitrogen at a temperature of −196° C.
Stored biological samples can be identified by writing on the disposable containers themselves, or by labels stuck to the containers. These labels may be handwritten or printed and can include bar codes. However, these methods of identification have associated disadvantages; written notes on containers can easily be erased or smudged and labels containing handwritten notes and printed text or barcode information can fall off the disposable containers while they are stored inside the Dewar leading to unidentifiable samples. These problems are exacerbated by the cold conditions in which biological samples must be kept.
When performing an audit of biological samples stored in cold storage (at temperatures of −196° C.), the samples should not be allowed to warm up to a temperature greater than −130° C. It is therefore desirable to minimise the amount of time spent outside of the Dewar wherever possible.
Recording, monitoring and auditing of samples in cold storage takes a considerable amount of time and effort, even when samples are labelled using barcodes. An additional and undesirable increase in the time taken to record or audit samples arises as a result of frost which forms on the surfaces of disposable containers and their labels when they are removed from liquid nitrogen into relatively warmer temperatures. It is common for samples to be stored for many years (e.g. 15 years) but even after just one year in storage, the layer of frost which builds up on a disposable container can make it impossible to make an optical reading of a bar code on a label using a bar code reader because a layer of frost blocks or diffracts the light of the bar code reader. The container cannot be warmed up to remove frost as this would lead to destruction of the sample. The frost can be wiped off the disposable container but this contributes to an undesirable increase in the amount of time taken to read the sample.
Where biological samples are stored in vials, it is common practice for multiple vials to be stored together in standardized boxes. Standardised boxes may have spaces for 100 vials in a 10×10 array or for 169 vials in a 13×13 array. It is also common, in a laboratory situation, for vials to be stored in a “test tube” rack having a 4×10 configuration. Many other configurations of n×m arrays exist. For example, a 3×3 array is often used for larger vials.
Commonly used sizes of vials include a diameter of 10 mm and a diameter of 12 mm although the diameter of the vial can be larger e.g. 25 mm.
It is known that Radio Frequency ID (RFID) tags can be used to monitor a plurality of vials stored at low temperatures of down to −196° C. An RFID reader can be used to write information to and read information from the RFID tag before, after, or during cryogenic storage.
An RFID tag includes an RF transmitter and an RF receiver. An RFID reader can be used to transmit an encoded radio signal to a tag to interrogate it. Upon receiving the interrogation signal, the RFID tag transmits its identification information to the reader. This identification information may be a unique serial number assigned to a particular patient or a particular sample.
In Europe and other countries outside of the US, RFID components for medical storage operate at an approved frequency of 13.56 MHz. It is important that the frequency used for the RFID tag does not lead to any undesirable interference with other electronic medical equipment. Lower medically approved frequency bands such as 125 KHz do not provide enough signal bandwidth to provide the tag with a useful user defined memory.
GB2456531 and EP2165287 disclose a monitoring system for monitoring a plurality of vials having RFID tags which work at frequencies of 13.56 MHz. Using the system described in these documents it is possible to associate an RFID tag on a vial with a particular box. However, it is not possible to monitor the exact location of the specific vial within the box.